1. Field of the Invention
This invention relates to a trocar used to form a hole in a body cavity during performance of thoracoscopic surgery or performance of laparoscopic surgery.
2. Description of the Related Art
A trocar generally comprises an obturator and a cannula. The obturator has a pyramid-shaped piercing tip at one end, and moves the piercing tip into tissue to form a hole to provide access to a body cavity. On the other hand, the cannula is located around the obturator. The cannula is inserted into the body cavity together with the obturator through the hole formed by the piercing tip. Such a trocar, therefore, forms a pathway in the inside of the cannula for inserting an endoscope or a surgical tool into the body cavity, by extracting or withdrawing the obturator from the cannula inserted into the body cavity.
When thoracoscopic surgery of the pneumothorax is required, the obturator and the cannula are inserted into a thoracic cavity through the patient's chest bones. Then, the obturator is extracted from the cannula, the surgical tool is inserted into the thoracic cavity through the cannula, and the surgical tool is brought near to the patient's lungs for performance of the pneumothorax treatment. In this case, it is difficult to get the surgical tool to approach to the back side of the lungs if the pneumothorax-inducing bulla is at the back side of the lungs.
When the bulla is at the back side of the lungs, therefore, it is desirable to use a surgical tool curved in a circular arc. But insertion of such a surgical tool into the thoracic cavity requires that the inside diameter of the cannula be formed to be larger than in prior art cannulas, since the cannula is formed in a straight shape and is formed of rigid materials such as stainless steel (see U.S. Pat. No. 5,053,016, U.S. Pat. No. 5,104,383). However, the insertion of the cannula into the thoracic cavity through the chest bones is difficult when the inside diameter of the cannula be formed to be larger than in the prior art cannulas.